Small-angle latch system for a lock

Abstract

A small angle latch is disclosed which moves a latch bolt from a fully extended position to a retracted position wherein the latch bolt is substantially flush with an outer surface of a faceplate through a rotation of an input device, such as a lever, in the range of from about 25 degrees to about 35 degrees, without exceeding a maximum torque upon the input member of 28 inch-pounds.

Claims

1. A latch system adapted to be drivingly connected to an input member of a lock assembly, the latch system comprising: a latch bolt housing defining an axis of reciprocation; a faceplate coupled to the latch bolt housing, the faceplate having a latch bolt opening which intersects the axis of reciprocation; a latch bolt having a latch bolt tip, the latch bolt being moveably disposed in the latch bolt housing for reciprocating movement along the axis of reciprocation; and a latch drive system adapted to couple the input member of the lock assembly to the latch bolt to move the latch bolt along the axis of reciprocation, the latch drive system including: a cam adapted to be connected for rotation with the input member, the cam rotating about an axis of rotation, the cam having an outer perimeter including a concave portion, a latch member disposed for reciprocating movement along the axis of reciprocation, the latch member including at least one protuberance positioned to be engaged with the cam, a drive member disposed in the latch bolt housing, the drive member having a convex portion arranged to be engaged by a portion of the latch member to pivot the drive member relative to the latch bolt housing against a protuberance formed on an interior surface of the latch bolt housing, the portion of the latch member being positioned between the drive member and the faceplate, and a latch bolt extension coupled to the latch bolt, the latch bolt extension having an arm positioned to be engaged by the drive member; the latch system having a rest configuration wherein the latch bolt is positioned in a fully extended position with the latch bolt tip extending a first distance from an outer surface of the faceplate in a direction away from the axis of rotation and an actuated configuration wherein in response to a system torque on the input member of the lock assembly the latch bolt tip moves towards the axis of rotation to a retracted position substantially flush with the outer surface of the faceplate, the protuberance of the latch member contacting the concave portion of the outer perimeter of the cam as the latch bolt moves from the extended position to the retracted position, the latch drive system moves the latch bolt from the extended position to the retracted position when the cam is rotated about the axis of rotation through a first angle of up to about 21 degrees; and wherein the protuberance of the latch member contacts the outer perimeter of the cam when the latch system is in the rest configuration.

2. The latch system of claim 1, wherein the protuberance of the latch member contacts the outer perimeter of the cam throughout the rotation of the cam through the first angle.

3. The latch system of claim 1, wherein the cam includes a cam aperture having a cam aperture perimeter surrounding the axis of rotation, the cam aperture having a cam rotation radius, the concave portion of the outer perimeter of the cam having a constant cam radius, a ratio of the cam radius of the concave portion of the outer perimeter of the cam to the cam rotation radius is at least 85%.

4. The latch system of claim 3, wherein the ratio of the cam radius of the concave portion of the outer perimeter of the cam to the cam rotation radius is at least 90%.

5. The latch system of claim 3, wherein the ratio of the cam radius of the concave portion of the outer perimeter of the cam to the cam rotation radius is about 100%.

6. The latch system of claim 1, wherein the concave portion of the outer perimeter of the cam has a variable radius.

7. The latch system of claim 1, wherein the first angle is in a range of from about 18 degrees to about 21 degrees.

8. The latch system of claim 1, wherein the movement of the latch bolt from the extended position to the retracted position is in response to a rotation of the input member of the lock assembly through a second angle in a range of about 25 degrees to about 35 degrees.

9. The latch system of claim 8, wherein a system torque of up to 28 inch-pounds upon the input member of the lock system is applied to result in the rotation of the input member of the lock assembly through the second angle.

10. The latch system of claim 8, wherein the second angle is about 25 degrees.

11. The latch system of claim 8, wherein the second angle is about 32 degrees.

12. The latch system of claim 1, further comprising a latch case connected to the latch bolt housing, the latch drive system disposed on the latch case.

13. The latch system of claim 12, wherein the latch case includes an opening, the cam extending through the opening of the latch case when the latch system is in the actuated configuration.

14. The latch system of claim 13, wherein a first component of the lock assembly contacts a second component of the lock assembly to prevent the cam from contacting an edge of the opening in the latch case, the first component of the lock assembly being spaced apart from the second component of the lock assembly when the latch system is in the rest configuration.

15. The latch system of claim 1, wherein the input member rotates about the axis of rotation defined by the cam.

16. The latch system of claim 1, wherein the axis of reciprocation is substantially perpendicular to the axis of rotation.

17. The latch system of claim 1, wherein the drive member has a generally U-shaped body having a pair of legs and a connecting base connecting a first leg of the pair of legs to a second leg of the pair of legs, the generally U-shaped body including a channel positioned between the pair of legs and having an open end and a closed end opposite the open end.

18. The latch system of claim 17, wherein the connecting base of the generally U-shaped body bears against a protuberance formed on an interior surface of the latch bolt housing as the drive member pivots relative to the latch bolt housing.

19. The latch system of claim 18, wherein the convex portion of the drive member includes a first convex bulge disposed on the first leg of the pair of legs and a second convex bulge disposed on the second leg of the pair of legs.

20. The latch system of claim 19, wherein each of the first convex bulge and the second convex bulge includes a first end and a second end positioned between the first end and the connecting base of the generally U-shaped body.

21. The latch system of claim 20, wherein the second end of the first convex bulge is collinear with the second end of the second convex bulge.

22. The latch system of claim 20, wherein a length of the first convex bulge from the first end of the first convex bulge to the second end of the first convex bulge is at least 40% of an overall length of the drive member from a tip of the first leg of the generally U-shaped body of the drive member to a lower extreme of the connecting base of the generally U-shaped base, the lower extreme of the connecting base being opposite the channel.

23. The latch system of claim 22, wherein the second convex bulge is identical to the first convex bulge.

24. The latch system of claim 1, wherein the protuberance of the latch member engages the concave portion of the outer perimeter of the cam member prior to the latch bolt moving from the extended position to the retracted position.

25. The latch system of claim 1, wherein the protuberance of the latch member contacts the concave portion of the outer perimeter of the cam member when the latch system is in the rest configuration.

26. A latch system adapted to be drivingly connected to an input member of a lock assembly, the latch system comprising: a latch bolt housing defining an axis of reciprocation; a faceplate coupled to the latch bolt housing, the faceplate having a latch bolt opening which intersects the axis of reciprocation; a latch bolt having a latch bolt tip, the latch bolt being moveably disposed in the latch bolt housing for reciprocating movement along the axis of reciprocation; and a latch drive system adapted to couple the input member of the lock assembly to the latch bolt to move the latch bolt along the axis of reciprocation, the latch drive system including: a cam adapted to be connected for rotation with the input member, the cam rotating about an axis of rotation, the cam having an outer perimeter including a concave portion, a latch member disposed for reciprocating movement along the axis of reciprocation, the latch member including at least one protuberance positioned to be engaged with the cam, a drive member disposed in the latch bolt housing, the drive member having a convex portion arranged to be engaged by a portion of the latch member to pivot the drive member relative to the latch bolt housing against a protuberance formed on an interior surface of the latch bolt housing, the portion of the latch member being positioned between the drive member and the faceplate, and a latch bolt extension coupled to the latch bolt, the latch bolt extension having an arm positioned to be engaged by the drive member; the latch system having a rest configuration wherein the latch bolt is positioned in a fully extended position with the latch bolt tip extending a first distance from an outer surface of the faceplate in a direction away from the axis of rotation and an actuated configuration wherein in response to a system torque on the input member of the lock assembly the latch bolt tip moves towards the axis of rotation to a retracted position substantially flush with the outer surface of the faceplate, the protuberance of the latch member contacting the concave portion of the outer perimeter of the cam as the latch bolt moves from the extended position to the retracted position, the latch drive system moves the latch bolt from the extended position to the retracted position when the cam is rotated about the axis of rotation through a first angle of up to about 21 degrees, wherein the outer perimeter of the cam contacts the protuberance of the latch member when the latch system is in the rest configuration at an initial point of contact, a drive vector passing through the axis of rotation and the initial point of contact forms a drive vector angle relative to horizontal in the range of from about 45 degrees to about 50 degrees.

27. The latch system of claim 26, wherein as the latch system moves to the actuated configuration, the drive vector angle increases.

28. The latch system of claim 26, wherein as the latch system moves to the actuated configuration, the drive vector angle remains an acute angle.

29. The latch system of claim 26, wherein the concave portion of the outer perimeter of the cam remains on a first side of a vertical plane passing through the axis of rotation as the latch system moves from the rest configuration to the actuated configuration, the drive member being positioned on the first side of the vertical plane.

30. A latch system adapted to be drivingly connected to an input member of a lock assembly, the latch system comprising: a latch bolt housing defining an axis of reciprocation; a faceplate coupled to the latch bolt housing, the faceplate having a latch bolt opening which intersects the axis of reciprocation; a latch bolt having a latch bolt tip, the latch bolt being moveably disposed in the latch bolt housing for reciprocating movement along the axis of reciprocation; and a latch drive system adapted to couple the input member of the lock assembly to the latch bolt to move the latch bolt along the axis of reciprocation, the latch drive system including: a cam adapted to be connected for rotation with the input member, the cam rotating about an axis of rotation, the cam having an outer perimeter including a concave portion, a latch member disposed for reciprocating movement along the axis of reciprocation, the latch member including at least one protuberance positioned to be engaged with the cam, a drive member disposed in the latch bolt housing, the drive member having a convex portion arranged to be engaged by a portion of the latch member to pivot the drive member relative to the latch bolt housing against a protuberance formed on an interior surface of the latch bolt housing, the portion of the latch member being positioned between the drive member and the faceplate, and a latch bolt extension coupled to the latch bolt, the latch bolt extension having an arm positioned to be engaged by the drive member; the latch system having a rest configuration wherein the latch bolt is positioned in a fully extended position with the latch bolt tip extending a first distance from an outer surface of the faceplate in a direction away from the axis of rotation and an actuated configuration wherein in response to a system torque on the input member of the lock assembly the latch bolt tip moves towards the axis of rotation to a retracted position substantially flush with the outer surface of the faceplate, the protuberance of the latch member contacting the concave portion of the outer perimeter of the cam as the latch bolt moves from the extended position to the retracted position, the latch drive system moves the latch bolt from the extended position to the retracted position when the cam is rotated about the axis of rotation through a first angle of up to about 21 degrees; wherein the protuberance of the latch member contacts the outer perimeter of the cam throughout the rotation of the cam through the first angle.

31. A latch system adapted to be drivingly connected to an input member of a lock assembly, the latch system comprising: a latch bolt housing defining an axis of reciprocation; a faceplate coupled to the latch bolt housing, the faceplate having a latch bolt opening which intersects the axis of reciprocation; a latch bolt having a latch bolt tip, the latch bolt being moveably disposed in the latch bolt housing for reciprocating movement along the axis of reciprocation; and a latch drive system adapted to couple the input member of the lock assembly to the latch bolt to move the latch bolt along the axis of reciprocation, the latch drive system including: a cam adapted to be connected for rotation with the input member, the cam rotating about an axis of rotation, the cam having an outer perimeter including a concave portion, a latch member disposed for reciprocating movement along the axis of reciprocation, the latch member including at least one protuberance positioned to be engaged with the cam, a drive member disposed in the latch bolt housing, the drive member having a convex portion arranged to be engaged by a portion of the latch member to pivot the drive member relative to the latch bolt housing against a protuberance formed on an interior surface of the latch bolt housing, the portion of the latch member being positioned between the drive member and the faceplate, and a latch bolt extension coupled to the latch bolt, the latch bolt extension having an arm positioned to be engaged by the drive member; the latch system having a rest configuration wherein the latch bolt is positioned in a fully extended position with the latch bolt tip extending a first distance from an outer surface of the faceplate in a direction away from the axis of rotation and an actuated configuration wherein in response to a system torque on the input member of the lock assembly the latch bolt tip moves towards the axis of rotation to a retracted position substantially flush with the outer surface of the faceplate, the protuberance of the latch member contacting the concave portion of the outer perimeter of the cam as the latch bolt moves from the extended position to the retracted position, the latch drive system moves the latch bolt from the extended position to the retracted position when the cam is rotated about the axis of rotation through a first angle of up to about 21 degrees; wherein the cam includes a cam aperture having a cam aperture perimeter surrounding the axis of rotation, the cam aperture having a cam rotation radius, the concave portion of the outer perimeter of the cam having a constant cam radius, a ratio of the cam radius of the concave portion of the outer perimeter of the cam to the cam rotation radius is at least 85%.

32. The latch system of claim 31, wherein the ratio of the cam radius of the concave portion of the outer perimeter of the cam to the cam rotation radius is at least 90%.

33. The latch system of claim 31, wherein the ratio of the cam radius of the concave portion of the outer perimeter of the cam to the cam rotation radius is about 100%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following descriptions of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

(2) FIG. 1 is a partially cut-away perspective view of one embodiment of a lock assembly embodying the small-angle latch system of the present invention, with the lever shown at rest and the latch system in the rest configuration which corresponds to the absence of external force on an input member of the lock assembly;

(3) FIG. 2 is a view similar to that of FIG. 1, with the lever having moved an angular distance of 8 degrees;

(4) FIG. 3 is a view similar to that of FIG. 2, with the lever having moved 31 degrees, and illustrating how the lever stops rotating before a cam engages a bottom plate of the latch of FIG. 1;

(5) FIG. 4 is an exploded perspective detail view of a lock assembly including the latch system of FIG. 1;

(6) FIG. 5 is an exploded perspective detail view of the latch system of FIG. 1, juxtaposed with a lever subassembly;

(7) FIG. 6 is an exploded perspective detail view of the latch system of FIG. 1;

(8) FIG. 7 is an assembled perspective view of the latch system of FIG. 1;

(9) FIG. 8 is an enlarged perspective detail view of the latch system of FIG. 1, illustrating the positions of the latch spring on the latch case, and further illustrating the inter-engagement of the latch spring with the latch member, as well as the latch member with the drive member;

(10) FIG. 9 is an enlarged perspective detail view of the latch system of FIG. 8, further showing the inter-engagement of the drive member with the latch bolt extension arms;

(11) FIG. 10 is an enlarged, partially cut-away elevational detail view (with the latch system of FIG. 1 axially rotated 90 degrees) showing the drive member of FIG. 9 being engaged by the latch member, the drive member in turn engages the bolt extension arms of the latch system of FIG. 1;

(12) FIG. 11A is a left side elevational detail view of the latch system of FIG. 1 at rest in the rest configuration with the latch bolt fully extended;

(13) FIG. 11B is a top plan view of the latch system of FIG. 11A, the latch system having been axially rotated 90 degrees from the position shown in FIG. 11A;

(14) FIG. 11C is a left side perspective view of the latch system of FIG. 11A;

(15) FIGS. 12A-12C are similar to FIGS. 11A-11C, respectively, but illustrating the latch system of FIG. 1 with the concave cam member having been rotated about half way through its total rotation angle of 18 degrees due to a rotation of the input member of the lock assembly;

(16) FIGS. 13A-13C are similar to FIGS. 11A-11C, respectively, but illustrating the latch system of FIG. 1 in the actuated configuration with the latch bolt fully retracted and the tip of the latch bolt being substantially flush with an outer surface of the faceplate;

(17) FIGS. 14, 15 and 16 are enlarged side elevational detail views of the latch system shown in FIGS. 11A, 12A, and 13A, respectively, and illustrate schematically the interaction of the concave cam member of the latch system of FIG. 1 with a protuberance of the latch member of the latch system of FIG. 1, and showing the resultant relatively low mechanical advantage generated by the small-angle latch system of FIG. 1;

(18) FIG. 17 is a front view of an exemplary cam of the latch system of FIG. 1; and

(19) FIGS. 18A and 18B are a front view and a sectional view of an exemplary drive member of the latch system of FIG. 1.

(20) Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the present invention, and such exemplifications are not to be construed as limiting the scope of the present invention in any manner.

DETAILED DESCRIPTION OF THE DRAWINGS

(21) With reference now to the drawings, in particular to FIGS. 1-18B thereof, apparatuses, systems, and methods embodying features, principles, and concepts of various exemplary embodiments of a small-angle latch system for a lock will be described. Referring now to FIGS. 1-4, an exemplary latch system 10 is connected by elongated tubular nuts 12 to an input member 14, illustratively a lever, of a lock assembly 16, such as a door lock. Other exemplary input members include knobs or other shapes having an exterior which may be grasped by an operator to rotate the input member.

(22) The latch system 10 is actuated by a square rod or square tube 18 extending from the lock assembly 16 through the latch system 10. Rotating the input member 14 about an axis of rotation 20 causes the square tube to rotate components of the latch system 10 to retract a latch bolt 28 so that it is substantially flush with a faceplate 26. As is particularly shown in FIG. 3, rotation of the lever 14 past a certain point is prevented by a first component of the lock assembly 16, illustratively an axially-extending portion 17 of a rotating plate 19, contacting a second component of the lock assembly 16, illustratively one of the elongated tubular nuts 12. This prevents a portion of cam 46 (see FIG. 3) from striking or “bottoming-out” against the bottom plate or latch case 21 of the latch system 10.

(23) Referring now to FIGS. 4-18B and particularly to FIGS. 5, 6, and 11A-11C, the small-angle latch system 10 includes a latch bolt housing 22 defining an axis of reciprocation 24, a faceplate 26, and a latch bolt 28 having a latch bolt tip 30. The latch bolt 28 is slidably disposed in the latch bolt housing 22 for reciprocating movement along the axis of reciprocation 24. The latch bolt 28 is biased to an extended position 36 by a latch spring 40. The latch case 21 is connected to the latch bolt housing 22 and supports a latch drive system 44, which couples the lever 14 with the latch bolt 28 to retract and extend the latch bolt. The latch drive system 44 includes a cam member 46 connected for rotation with the lever 14, a latch member 48 having at least one latch member protuberance 49 and engaged with the cam member 46, and a drive member 50 that pivots on the latch member 48. In the embodiment shown, the cam member 46 is made of two matching parts. However, in additional embodiments, the cam member 46 may be formed as a single piece.

(24) Also, in the embodiment shown, the latch member 48 has two protuberances 49, so that the cam member 46 may engage the latch member whether the handle 14 is rotated clockwise or counterclockwise. In other embodiments, the latch member 48 may have a single protuberance 49. The latch drive system 44 also includes a latch plate or bolt extension 52 defining two bolt extension arms 53. The latch bolt extension 52 is connected to the latch bolt 28, such that rotation of the cam member 46 against the latch member protuberance 49 causes the latch member 48 to pivot the drive member 50 against the latch bolt extension 52 via the bolt extension arms 53 to retract the latch bolt 28 (see FIGS. 8-11C). The drive member 50 pivots about an interior protuberance 51 (see FIG. 10) formed on an inside surface of the latch bolt housing 22.

(25) The cam member 46 is directly connected to the square tube 18, such that rotation of the lever 14 rotates the square tube, which in turn rotates the cam member 46. As shown in FIGS. 11A-11C, and particularly in FIGS. 11A and 17, the cam member 46 has a perimeter 56 including a concave cam surface 54 drivingly engaged with the latch member protuberance 49. The cooperation of the above-noted elements of this embodiment will retract the latch bolt 28 to the retracted position 38 with a rotation of the lever 14 through an angle in the range of from about 25 degrees through about 35 degrees, depending upon whether the latch is a passage-type system or an entrance-type system, without the system torque exceeding 28 inch-pounds. In another embodiment, the lever rotation in a passage-type system may be as low as 25 degrees-26 degrees, and in an entrance-type system, as low as 32 degrees-33 degrees, to retract the latch bolt 28.

(26) Referring to FIG. 17, concave cam member 46 includes a cam aperture 64 which receives tube 18 (see FIG. 1). Cam aperture 64 is bounded by a perimeter wall 66 having a cam rotation radius which is one-half of the largest diameter of the cam aperture 64, indicated by diameter 68 in FIG. 17. The concave cam surface 54 of cam 46 may be circular and define a constant cam radius, such that the ratio of the cam radius to the cam rotation radius may be greater than or equal to 85%. In another embodiment, the ratio may be greater than or equal to 90%. In still another embodiment, the ratio may be substantially equal to 100%. In one example, the radius of concave cam surface 54 is 5.0 millimeters. Furthermore, in yet another embodiment, the concave cam surface may be defined by a variable radius.

(27) In yet another embodiment, the concave cam member 46 may define a cam member center of rotation 60 coincident with the axis of rotation 20 of the lever 14.

(28) As shown in FIGS. 18A and 18B, the drive member 50 of latch system 10 may have a generally “U”-shaped configuration and define an open end and a closed end. The open end of the “U” includes two legs, on each of which is disposed a convex bulge 70 having a first end 71 and a second end 73. The convex bulges 70 are substantially parallel and include respective collinear lower edges at second end 73. The drive member may further include a central aperture 74 having a closed end 76 and an open end 78. Closed end 76, in one example, is collinear with the lower edges 73 of the convex bulges 70 and in another example, is offset from the lower edges 73 of the convex bulges. The convex bulges 70 engage latch member 48 and drive member 50 further engages bolt extension arms 53. The dimensions and orientation of the convex bulges 70, and the positions of the bulges 70 relative to the closed end 76 of the aperture 74 and to the bolt extension arms 53, are configured to cooperate with the concave cam member 46 of the latch system 10 to fully retract the latch bolt 28 when the cam member rotates 21 degrees or less, and even as little as 18 degrees, responsive to rotation of the lever 14. In one example, a length of each convex bulge 70 from the first end 71 to the second end 73 is at least 40% of an overall length of the drive member 50 from a tip of the first leg of the generally U-shaped body of the drive member 50 to a lower extreme of a connecting base of the generally U-shaped base connecting the two legs, the lower extreme of the connecting base being opposite the channel. In a further example, a ratio of (a) the difference of one half of the diameter of the drive member 50 minus a length of the connecting base of the drive member 50 along the centerline plane of the drive member over (b) one half of the diameter of the drive member is at least 40%.

(29) As shown in FIGS. 11A, 12A and 13A, a line L drawn through the center of rotation 20 to a point of contact 62 with the protuberance 49, stays to a first side of vertical plane passing through a line 200 which passes through the axis of rotation 20 as the latch bolt 28 is retracted, so that the contact point 62 remains between the vertical plane defined by line 200 and faceplate 26. However, in other embodiments, it may be desirable not to require that all points of contact 62 occur to the left of vertical line 200, depending upon the configurations and dimensions of for example, the cam member 46 and latch member 48.

(30) Referring to FIGS. 14-16, for purposes of illustration, a line drawn from the axis of rotation 20 of the lever 14 (which access is coincident with the axis or center of rotation 60 of convex cam member 46), to a point of contact 62 of the convex cam member with a protuberance 49 of the latch member 48, is representative of the direction of the force exerted by the lever 14 in rotating the cam member 46 against the latch member 48. This line is designated “drive vector Vn.” FIG. 14 corresponds to the rest configuration of latch system 10 and FIG. 11A. FIGS. 15 and 16 correspond to FIGS. 12A and 13A, respectively. As shown in FIG. 14, cam 46 contacts protuberance 49 when latch system 10 is in the rest configuration and throughout movement to the actuated configuration shown in FIG. 16.

(31) As schematically shown in the force diagrams, Dn, in FIGS. 14-16, as the point of contact 62 of cam surface 54 progressively begins to slide “down” ‘the concave cam curve, the horizontal component of the force Fn is relatively small, compared conventional latch systems resulting in the torque required to rotate a lever 14 being larger in latch system 10 relative to conventional latch systems. However, as a result of the configuration of latch system 10, the torque upon the lever 14 remains below a limit of 28 inch-pounds. As the lever 14 rotates, the horizontal component of the force Fn increases, but still remains relatively small compared to that generated by a conventional latch system.

(32) As shown, for example, in FIG. 14, the initial angle An of the drive vector Vn relative to the horizontal of the latch system 10 of the present invention, has been selected to be about 50 degrees. However, in other embodiments, the initial angle An may be selected to be any angle equal to or greater than 45 degrees, depending upon the dimensions and configurations of such system elements as cam 46 and latch member 48.

(33) Referring to FIG. 11A, in the rest configuration, latch bolt 28 is fully extended by a distance 100 from an outer surface of faceplate 26. In one example, distance 100 is 12 millimeters. The line, L, makes an angle 102 having a value of 50 degrees relative to horizontal and the drive member 50 makes an angle 104 having a value of 61 degrees relative to horizontal. Referring to FIG. 12A, cam 46 is rotated an angle 106 having a value of 9 degrees which results in angle 102 having an increasing value to 63 degrees, angle 104 having an increasing value to 78 degrees, and distance 100 having a decreasing value to 7.3 millimeters. Referring to FIG. 13A, cam 46 is rotated an angle 106 having a value of 18 degrees to the actuated configuration wherein the latch bolt 28 is fully retracted which results in angle 102 having an increasing value to 78 degrees, angle 104 having an increasing value to 110 degrees, and distance 100 having a decreasing value to 0.6 millimeters.

(34) It has been discovered that if the initial point of contact of a cam with the latch member were configured to occur as far to one side (such as the left) as possible of the center of rotation of the lever/cam, then a smaller amount of lever rotational angle would horizontally translate the latch member through approximately the same distance as is traveled by the latch member of a conventional system, resulting in full retraction of the latch bolt.

(35) It has further been discovered that by using a cam member with a concave cam surface to engage the latch member initially at a relatively shallow angle (producing a relatively low mechanical advantage, and thus requiring a relatively high initial torque to be placed on the lever), a significantly higher amount of latch bolt retraction could be achieved per unit of lever or knob rotation. Therefore, in an entrance-type lock, for example, a lever rotation as small as 32 degrees could be obtained without exceeding 28 inch-pounds of torque on the lever. This represents almost a 40% reduction in lever rotation from a conventional system. In a passage-type lock, the lever rotation angle can be reduced to as little as 25 degrees.

(36) Accordingly, in one embodiment, a latch system is drivingly connected to a lever or knob of a lock assembly, where the lever or knob defines an axis of rotation. The latch system further includes a latch bolt housing defining an axis of reciprocation, and a faceplate attached to the latch bolt housing. A latch bolt having a latch bolt tip is slidably disposed in the latch bolt housing for reciprocating movement along the axis of reciprocation between an extended position and a retracted position, the retracted position defined by the latch bolt tip being substantially flush with the faceplate. The latch bolt is biased to the extended position by a latch spring. The small-angle latch system further includes a latch case connected to the latch bolt housing, and a latch drive system disposed on the latch case and operatively associated with the lock lever or knob. The latch drive system couples the lever or knob with the latch bolt to retract and extend the latch bolt. The latch drive system produces a system torque, which is measured at the lever when rotation of the lever retracts the latch bolt to the retracted position. The latch drive system further includes a cam member connected for rotation with the lever, a latch member engaged with the cam member, a drive member disposed for pivoting movement on the latch member, and a bolt extension connected to the latch bolt and operatively associated with the drive member, such that rotation of the earn member causes the latch member to pivot the drive member against the bolt extension to retract the latch bolt. The cam member includes a concave cam surface drivingly engaged with the latch member. The cooperation of the above-noted elements of this embodiment of the present invention will retract the latch bolt to the retracted position with a rotation of the lever through an angle in the range of from only about 25 degrees through about 35 degrees, depending upon whether the latch is a passage-type system or an entrance-type system, without the system torque upon the lever exceeding 28 inch-pounds.

(37) In another embodiment, the cam member may include a cam aperture having a cam rotation radius, and is operatively associated with the lever. The concave cam surface may be circular and define a constant cam radius, such that the ratio of the earn radius to the cam rotation radius is greater than or equal to 85%. In still another embodiment, the ratio may be greater than or equal to 90%. In yet another embodiment, the ratio may be substantially equal to 100%. In a further embodiment, the cam surface may be defined by a variable radius.

(38) In yet another embodiment, the lever may retract the latch bolt to its retracted position when the concave cam member rotates 21 degrees or less responsive to rotation of the lever, still without the system torque exceeding 28 inch-pounds upon the lever. In still another embodiment, the lever may retract the latch bolt to its retracted position when the concave cam member rotates through a range of from about 18 degrees to about 21 degrees. In yet another embodiment, the cam surface immediately begins moving the latch member when the lever starts to turn, so that there is no lost motion.

(39) In another embodiment, the concave cam member may define a cam member center of rotation coincident with the center of rotation of the lever. The concave cam surface engages the latch member at a point of contact, such as a latch member protuberance. The initial point of contact occurs when the latch bolt is fully extended, and is configured so that a drive vector extending from the center of rotation of the concave cam member to the initial point of contact, may be disposed at an angle in the range of from about 45 degrees to about 50 degrees to the horizontal (a line parallel to the axis of reciprocation of the latch member) (“drive vector angle”). In yet another embodiment, when the lever retracts the latch bolt to its retracted position, the drive vector angle may rotate through a total angle of about 78 degrees. In a further embodiment, during the operation of the small-angle latch system of the present invention, the drive vector angle may remain an acute angle. In yet another embodiment, the points of contact of the concave cam surface with the latch member will remain to the left of a vertical line drawn through the center of the axis of rotation of the cam member.

(40) In still another embodiment, the drive member may have a generally “U”-shaped configuration and define an open end and a closed end. The closed end of the “U” bears against a protuberance formed on an interior surface of the latch bolt housing as the drive member pivots on the latch member. The open end of the “U” includes two legs, on each of which is disposed a convex bulge. The convex bulges are substantially parallel and include respective collinear lower edges. The drive member may further include a central aperture having a closed end and an open end. The convex bulges engage respective arms formed on the bolt extension. The dimensions and orientation of the convex bulges, and the positions of the bulges relative to the closed end of the aperture and to the bolt extension arms, may be configured to cooperate with the concave cam member to fully retract the latch bolt when the cam member rotates through an angle in the range of from about 18 degrees to about 21 degrees, responsive to rotation of the lever.

(41) In yet another embodiment, a method of retracting a latch bolt for a lock assembly having a lever operatively associated with the cam member, where the axis of rotation of the lever and cam member are coincident, may include disposing a latch member relative to the center of rotation of the lever and cam member, so that during the operation of the lock assembly, the point of contact of the cam member with the latch member remains on one side of a vertical line drawn from the latch member through the axis of rotation.

(42) In a further embodiment, a method of minimizing the amount of rotation required for a lever of a lock assembly to retract the lock assembly latch bolt, while utilizing the same physical envelope of a conventional latch system, may include disposing a cam member having a concave cam surface, and a latch member operatively associated with the earn member, in the conventional latch system envelope so that the handle rotation lies in the range of from about 25 degrees through about 35 degrees, without exceeding a maximum torque upon the lever of 28 inch-pounds.

(43) In yet another embodiment, a method for retracting a latch bolt to its retracted position in a small-angle tubular latch system of a lock assembly having a lever, where the lever defines an axis of rotation, where the lever is operatively associated with a latch member disposed for reciprocating movement along an axis of reciprocation, and where the latch member is operatively associated with the latch bolt, may include engaging a concave cam surface with the latch member so that rotation of the lever through an angle in the range of from about 32 degrees through about 35 degrees may retract the latch bolt to its retracted position. In still another embodiment, the method may include disposing the cam surface on a cam member having an axis of rotation coincident with the axis of rotation of the lever; engaging the cam surface with the latch member at an angle in the range of from about 45 degrees to about 50 degrees to the horizontal with a drive vector intersecting the center of rotation and the point of engagement of the cam surface with the latch member, thereby creating a drive vector angle: and rotating the lever so that the vector angle increases to about 78 degrees.

(44) In yet another embodiment, the method may include rotating the cam member through a total angle in the range of from about 18 degrees to about 21 degrees, while maintaining the torque on the lever at or below 28 inch-pounds.

(45) By this point, it can be seen that the latch system of the present invention, in contravention of conventional engineering best practices, has been able to significantly reduce the amount of lever rotation required to retract the latch bolt, without exceeding the maximum torque limit of 28 inch-pounds. It can also be seen that this new latch system can be readily emplaced in the physical envelope of the conventional lock and latch system with a minimum of modifications to the structure of the conventional lock and latch system.

(46) While this invention has been described as having exemplary designs, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.